Membrane Fouling Mechanism Of Different Statuses Of Biomass In MBBR-MBR And SG-MBR

In this paper,a comparative experiment was used to run two reactors at the same time.One was a traditional membrane bioreactor(MBR).Because of the complete suspended growth of activated sludge in the reactor,it is referred to as an suspended-growth membrane bioreactor(SG-MBR).The other was a moving bed biofilm reactor-membrane bioreactor(MBBR-MBR).This work aimed at illustrating the mechanism of the influence of different statuses of biomass on filtration resistance and membrane fouling components in MBBR-MBR and SG-MBR.The two reactors were operated simultaneously under the same conditions to treat synthetic wastewater.Compared with SG-MBR,a high-density polyethylene(HDPE)suspension bio-carriers with a 35% filling ratio was placed in the MBBR-MBR.In addition,in the MBBR-MBR,due to the presence of bio-carriers,the form of activated sludge in the reactor has changed,ie,part of the sludge has grown in suspension and the other part of the sludge has grown attached.Both reactors were operated in parallel for 90 days.During this period,the treatment effect of the MBRs on synthetic wastewater was studied and their operating characteristics and the accumulated membrane foulants were comparatively studied by using multi-methods.The main findings were as follows:By continuously operating two different MBRs for 90 days under the same experimental conditions with no sludge discharge,the membrane fouling caused by the biomasses in MBRs with different growing statuses was compared to reveal the essential reasons leading to membrane fouling.Combining with the results of performance of the used MBRs and the characteristics of membrane foultants revealed by multi-method,the following conclusions could be drawn: Adding bio-carriers into an MBR is an effective approach to mitigate membrane fouling.During the same time period of operation(78days),when the trans-membrane pressure(TMP)value of the bioreactor with bio-carriers reached 32.5 kPa for the first time,the trans-membrane pressure value of the bioreactor without bio-carriers had reached 32.5 kPa for the third time.That is,during the same periodof operation,the MBR with bio-carriers only needed once to wash the membrane module,while,it needed for three times for the MBR with no bio-carriers.The added bio-carriers could effectively inhibit the formation of the reversible and the permanent resistance on membrane surface,especially the former.The added bio-carriers decreased the deposition of membrane foulants,such as extracellular polymeric substances(EPS)and soluble microbial products(SMP).On the 78 th day,the concentration of SMP and EPS in membrane surface contaminants in MBBR-MBR was 40.28 and 30.19 mg/g TVSS,respectively,while the concentration of SMP and EPS in membrane contaminants in SG-MBR was 41.01 and 37.97 mg/g TVSS.In addition,this study also found that the sludge particle size in MBBR-MBR was significantly larger than that in SG-MBR,so in order to confirm whether or not an aerobic granular sludge could be formed in MBBR-MBR(Aerobic Granular Sludge,AGS),further studied the formation mechanism of granular sludge and its effect on membrane fouling.After the end of the experiment,two MBBR-MBR reactors were re-run and compared with the filling ratios of 30% and 50%,respectively.The results showed that different colors of granular sludge appeared in the two MBBR-MBRs.In the low-fill reactor,the granular sludge appeared after the biofilm came off,and the formation mechanism was different from the traditional granular sludge formation mechanism.And the emergence of granular sludge to a certain extent slowed the rate of membrane fouling.In summary,this study showed that the addition of bio-carriers in the MBR not only improved the wastewater treatment efficiency of the reactor,but also effectively mitigated membrane fouling.